Machines such as, for example, wheel loaders, track type tractors, and other types of heavy machinery can be used for a variety of tasks. These machines include a power source, which may be, for example, an engine, such as a diesel engine, gasoline engine, or natural gas engine that provides the power required to complete such tasks. To effectively perform such tasks, the machines also include one or more implements, and at least one hydraulic pump driven by the power source. The hydraulic pump is typically fluidly connected to one or more hydraulic cylinders associated with each implement, and movement of each implement can be controlled by directing hydraulic fluid to and/or removing hydraulic fluid from such cylinders.
When an implement is lowered during performance of such tasks, the pressurized hydraulic fluid within the corresponding hydraulic cylinders is typically discharged to a fluid reservoir or tank. Such pressurized hydraulic fluid, however, contains energy that could be utilized by components of the machine to perform additional tasks. However, many known machines have no means of recovering such energy when the hydraulic cylinder is retracted during implement lowering. Instead, such machines typically throttle the fluid through one or more valves to control a lowering speed of the implement and/or a retracting speed of the hydraulic cylinder. This throttling results in a waste of energy and undesired heating of the hydraulic fluid as it passes to the tank. Additionally, this heat must eventually be removed by a cooling system of the machine, and as a result, such heat generation decreases the operational efficiency of the machine.
Some attempts have been made to recover this otherwise wasted energy. For example, International Publication No. WO 00/00748 discloses a system that recovers energy by providing an additional pump/motor with an over-center capability in the hydraulic circuit. The pump/motor transfers fluid between a lifting circuit and an accumulator for storing energy. However, when the lifting cylinder is dropped rapidly, a large quantity of fluid is discharged rapidly from the cylinder. To accommodate the fluid, the pump/motor needs to be large. Additionally, when the lifting cylinder is being retracted and the accumulator is at a higher pressure than the fluid discharged from the lift cylinder, additional energy from the engine is required to store the energy coining from the lift cylinder. Requiring such additional energy from the engine for the purposes of energy storage reduces the operational efficiency of the machine.
The disclosed systems and methods are directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.